Forb community response to prescribed fire, livestock grazing, and an invasive annual grass in the Pacific Northwest Bunchgrass Prairie

Abstract

Questions: Grassland degradation due to agriculture, changing fire regimes, and invasive species negatively affects forb communities. Conserving forbs and the services they provide requires a better understanding of their responses to interacting disturbances. Although fire and livestock grazing are important disturbances, their effect on forb communities in the Pacific Northwest Bunchgrass Prairies is not fully understood. Our objectives were to: (a) determine how prescribed fire and livestock grazing influence forb community composition, cover, species richness, and diversity over a 10-year span; (b) identify indicator species for each treatment; and (c) quantify forb responses to increasing cover of the invasive grass Ventenata dubia.

Forgotten forbs: Standard vegetation surveys underrepresent ecologically and culturally important forbs in a threatened grassland ecosystem

“…Therefore, the status and trends of forb richness and abundance are largely unknown, and current management practices rely on and are informed by, research evaluating vegetation responses measured in the summer. For example, research on PNB vegetation dynamics and grassland responses to herbicide, fire, livestock grazing, and invasive species (e.g., Averett et al, 2020; Endress et al, 2012; Taylor et al, 2013; Watson et al, 2021) utilize data collected during summer to draw conclusions, inferences and management recommendations. Relying on results generated from summer sampling either ignores spring‐dominant species responses (including most perennial forbs in PNB) or implicitly assumes that management practices (e.g., prescribed fire) implemented based on the beneficial responses of summer‐dominant species are also beneficial to spring‐dominant forbs.…”

“…Of the more than 2500 vegetation surveys conducted by the US Forest Service in mid-elevation grassland and shrubland communities in eastern Oregon during the past 40 years, just 11% were conducted prior to June (Figure 2; Averett & Endress, 2022b). Additionally, published research on forbs, grassland floristics, or vegetation dynamics are largely based on summer sampling efforts (e.g., Averett et al, 2020;Endress et al, 2020;Taylor et al, 2013;Tubbesing et al, 2014;Watson et al, 2021), with the few exceptions restricted to descriptive narratives (Daubenmire 1942, Tisdale, 1982.…”

Pre‐fire grazing and herbicide treatments can affect post‐fire vegetation in a Great Basin rangeland

“…Much research has been devoted to understanding the effects of livestock grazing on rangeland plant communities. However, despite a logical link between targeted grazing and fire management, there is a small but growing pool of research dedicated to understanding how wildfire and pre-fire grazing might interact (Davies et al, 2016(Davies et al, , 2021Ridder et al, 2022;Watson et al, 2021). Grazing is expected to be useful for reducing fuel loads at key times of the year while also shifting plant species composition and competition dynamics.…”

Forb composition gradients and intra‐annual variation in a threatened Pacific Northwest Bunchgrass Prairie

“…Current knowledge of vegetation ecology and trends in the PNB are based on the dominant bunchgrass species. Past forb research in the PNB have included descriptions of dominant forb species relationships to bunchgrass compositional gradients (Daubenmire, 1942 ; Johnson & Simon, 1987 ; Johnson & Swanson, 2005 ; Tisdale, 1982 ), grazing, prescribed fire and non‐native annual grass invasion (Watson et al, 2021 ), and autecology of specific forbs (U.S. Fish and Wildlife Service, 2007 ; Taylor et al, 2012 ; Tubbesing et al, 2014 ; Weaver, 1915 ).…”

“…Current knowledge of vegetation ecology and trends in the PNB are based on the dominant bunchgrass species. Past forb research in the PNB have included descriptions of dominant forb species relationships to bunchgrass compositional gradients (Daubenmire, 1942;Johnson & Simon, 1987;Johnson & Swanson, 2005;Tisdale, 1982), grazing, prescribed fire and non-native annual grass invasion (Watson et al, 2021), and autecology of specific forbs (U.S. Fish and Wildlife Service, 2007;Taylor et al, 2012;Tubbesing et al, 2014;Weaver, 1915). Yet, there are substantial knowledge gaps related to forb community dynamics and gradients in the PNB, particularly with regard to spring ephemeral species-species whose growth occurs early in the spring and senesce by summer and are abundant in the PNB (Daubenmire, 1942;Tisdale, 1982).…”